Cystic Fibrosis (CF) is the number one genetic cause of death in the Caucasian population affecting a in 2000 births and is an obvious candidate disease for gene therapy. Despite recent successes in the ability to transfer the CFTR gene to the lung of CF patients using recombinant adenoviruses, little in known about the underlying pathophysiologic mechanisms which lead to the development of chronic bacterial infections and unavoidable morbidity of this lung disease. Critical to the evaluation of current gene therapy efforts for CF lung disease is a concrete understanding of lung pathophysiology and primary defects. In addition, the development of animal models to evaluate methods of gene replacement will be crucial in determining complementation efficacy of primary defects in clinical trials. Without such functional end-points of complementation, incremental benefit of lung function from clinical efficacy trials will be difficult to interpret in the already damaged lungs of adults. Such a patient population is the likely target of phase II trials which evaluate the efficacy of adenoviral vectors will be performed in adults in which irreversible damage such as bronchiectasis has already occurred. Hence, clinical end-points for efficacy must be sensitive as well as relevant to the pathogenesis of lung disease. Several primary defects in CF airways have been postulated to contribute to the pathology of this disease including defects in apical Cl secretion, Na hyperabsorption, altered fluid transport, and mucous biochemistry. However, the pathophysiologic relevance of each of these defects in the contribution of bacterial colonization of the CF airways remains unclear. Nor is it clear what level of transgene correction or targeting is necessary to achieve efficacious therapies by reversal of these primary defects. To this end, we have developed two models, the a human bronchial xenograft model of the CF and non-CF proximal airway and the CF transgenic mouse, which will allow for the elucidation of several potential primary defects in CF airway epithelium as well as the evaluation of CFTR gene replacement to correct these defects. The first component of this proposal attempt to evaluate several functional defects in 1) Cl and Na transport (using transepithelial potential difference measurements), 2) fluid transport and composition, 3) biochemical defects in mucus, and 4) bacterial finding to epithelial cells and secreted mucus. Within the second component of this proposal, these models will in turn be used to preclinically evaluate recombinant adenoviruses for the extent of complementation of these primary defects. Such studies will not only provide insights into the pathophysiologic mechanisms by which the CF airway is predisposition to bacterial colonization but will also prove useful in evaluating efficacy of adenoviral vectors developed for gene replacement in CF lung disease.